The present invention relates to an apparatus and a method for detecting a current direction in bridge circuits and more particularly to an apparatus and a method for detecting current direction in a PWM converter or an inverter.
To an inverter or a converter, its load always presents a resistor-inductive character. As a result, a phase angle exists between a load current and an output voltage of the inverter or converter that varies with output frequency and load conditions. In many cases, a current direction is required to control the conduction or non-conduction of electronic switches in the inverter or converter. For example, the phase angle between the load current and the output voltage can be calculated from the current direction when a voltage phase is known. Besides, in dead time compensation, the current direction indicates the polarity of a distortion voltage caused by the dead time. Furthermore, the current direction can also be used to judge whether the output current is zero or includes a DC component.
Please refer to FIG. 1. FIG. 1 is a block diagram of a current direction detecting circuit in an inverter or a converter according to the prior art. As shown in FIG. 1, the current direction of the converter or converter is acquired by means of a HALL sensor 101. Other known devices, such as current transformers, can be similarly used to detect the current direction of the converter or converter. However, these devices are known to have the following drawbacks: a) a high cost; and b) the low precision caused by the magnetic hysteresis effect and offset due to temperature. FIG. 2 shows another typical circuit to get the current direction of the inverter or converter. In the figure, the current direction of the inverter or converter can be indicated according to the magnitude of a voltage across a resistor sensor 102. However, when the current is very small, especially around a zero crossing point of the current, the voltage across the resistor sensor 102 is small and therefore the current direction of the inverter or converter is hard to be detected by the resistor sensor 102 because of the effect of the noise and transient noise generated by PWM chopping. Consequently, to improve this problem, the resistor sensor 102 has to be selected a large value so that the power loss on the resistor sensor rises greatly. When a large power capacity of the inverter or converter is employed, the power loss of the resistor sensor will consume too much.
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.
It is therefore an object of the present invention to propose an apparatus and a method for detecting the current direction of an inverter or a converter with a high accuracy, high reliability, and low cost circuit.
It is another object of the present invention to propose an apparatus and a method for detecting a phase angle between an output voltage and an output current of an inverter or a converter.
It is a further object of the present invention to propose an apparatus and a method for indicating whether the output current is zero or includes a DC component.
In accordance with an aspect of the present invention, the current direction detecting apparatus having at least one phase bridges formed by a series connection of electronic switches, each of which is formed by a switching device in anti-parallel with a diode, a first node between the electronic switches electrically connected to a load, one end of the phase bridge electrically connected to one end of a first DC power supply, and the other end of the phase bridge electrically connected to the other end of the first DC power supply, including a diode having a cathode end electrically connected to the first node between the electronic switches, a resistor having one end electrically connected to an anode end of the diode to form a second node and the other end electrically connected to a second DC power supply, and a comparator having one of its input ends electrically connected to the anode of the diode and the other input end electrically connected to a predetermined voltage level, wherein a current direction of the first node is determined by an output signal of the comparator.
Preferably, the current direction detecting apparatus is applied to an inverter.
Preferably, the current direction detecting apparatus is applied to a converter.
Preferably, the current flows out the first node when the output signal of the comparator is at a high level and the current flows into the first node when the output signal of the comparator is at a low level.
Preferably, the current flows out the first node when the output signal of the comparator is at a low level and the current flows into the first node when the output signal of the comparator is at a high level.
Preferably, the current direction detecting apparatus further includes a sampler with its input end electrically connected to an output end of the comparator, and a sampling action is carried out during an interval that a gate driver signal of a lower switching device of the phase bridge is enabled.
Preferably, the current direction detecting apparatus further includes an isolator added between the output end of the comparator and the input end of the sampler.
Preferably, a sampling action is carried out during an interval that a gate driver signal of an upper switching device of the phase bridge is disenabled.
Preferably, the phase bridge includes an upper arm that is an upper switching device and a lower arm, which is a lower switching device.
Preferably, the current direction detecting apparatus further includes a decomposing device electrically connected to the anode of the diode for outputting a current direction signal by identifying a low level voltage of the voltage series at the second node in accordance with a gate driver signal of the phase bridges.
Certainly, a phase angle between an exciting voltage and an output current can be obtained if a voltage direction is known.
Certainly, the current direction detecting apparatus can detect whether the output current has a DC component.
In accordance with another aspect of the present invention, the current direction detecting apparatus having at least one phase bridges formed by a series connection of electronic switches, each of which is formed by a switching device in anti-parallel with a diode, a first node between the electronic switches electrically connected to a load, one end of the phase bridges electrically connected to one end of a first DC power supply, and the other end of the phase bridges electrically connected to the other end of the first DC power supply, including a diode having a cathode end electrically connected to a second DC power supply, a resistor having one end electrically connected to the first node between the electronic switches and the other end electrically connected to an anode end of the diode to form a second node, and a comparator having one of its input ends electrically connected to the second node and the other input end electrically connected to a predetermined voltage level, wherein a current direction of the first node is determined by an output signal of the comparator.
Preferably, the current direction detecting apparatus is applied to an inverter.
Preferably, the current direction detecting apparatus is applied to a converter.
Preferably, the current flows out the first node when the output signal of the comparator is at a high level and the current flows into the first node when the output signal of the comparator is at a low level.
Preferably, the current flows out the first node when the output signal of the comparator is at a low level and the current flows into the first node when the output signal of the comparator is at a high level.
Preferably, the current direction detecting apparatus further includes a sampler with its input end connected to an output end of the comparator, and the sampling action is carried out during an interval that a gate driver signal of the lower phase bridge switching device is enabled.
Preferably, the current direction detecting apparatus further includes an isolator added between the output end of the comparator and the input end of the sampler.
Preferably, a sampling action is carried out during an interval that a gate driver signal of an upper switching device of the phase bridge is disenabled.
Certainly, a phase angle between an exciting voltage and an output current can be obtained if a voltage direction is known.
Certainly, the current direction detecting apparatus can detect whether the output current has a DC component.
It is therefore further aspect of the present invention to propose a current direction detecting method applied to a phase bridge having a series connection of electronic switches, each of which is formed by a switching device in anti-parallel with a diode, a first node between the electronic switches electrically connected to a load, one end of the phase bridge electrically connected to one end of a first DC power supply, and the other end of the phase bridge electrically connected to the other end of the first DC power supply, including the steps of providing a diode having a cathode end electrically connected to the first node between the electronic switches, and providing a resistor having one end electrically connected to an anode end of the diode to form a second node and the other end electrically connected to a second DC power supply, wherein a current direction of the first node is determined by a magnitude of a signal at the second node.
It is therefore additional aspect of the present invention to propose a current direction detecting method applied to a phase bridge having a series connection of electronic switches, each of which is formed by a switching device in anti-parallel with a diode, a first node between the electric switches electrically connected to a load, one end of the phase bridges electrically connected to one end of a first DC power supply, and the other end of the phase bridges electrically connected to the other end of the first DC power supply, including the steps of providing a diode having a cathode end electrically connected to a second DC power supply, and providing a resistor having one end electrically connected to the first node between the electronic switches and the other end electrically connected to an anode end of the diode to form a second node; wherein a current direction of the first node is determined by a magnitude of a signal at the second node.
Preferably, the current direction detecting method further includes the step of: obtaining a phase angle between an exciting voltage and an output current if a voltage direction is known.
Preferably, the current direction detecting method further including the step of detecting whether the output current has a DC component current or not.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: